Revert to original main-template without pod downtime

[jjngx]

Proposed changes

This PR introduces the following changes:

• when a user deletes custom main-template from the ConfigMap obj, NIC will revert to the original, default template
• there is no need to restart NIC pod and introduce downtime anymore

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Testing:

• deploy NIC and verify initial ConfigMap:

➜  common git:(fix/github-5906) ✗ k describe configmaps -n nginx-ingress nginx-config
Name:         nginx-config
Namespace:    nginx-ingress
Labels:       <none>
Annotations:  <none>

Data
====

BinaryData
====

Events:
  Type    Reason   Age                From                      Message
  ----    ------   ----               ----                      -------
  Normal  Updated  42m (x9 over 20h)  nginx-ingress-controller  Configuration from nginx-ingress/nginx-config was updated
  Normal  Updated  31m (x3 over 35m)  nginx-ingress-controller  Configuration from nginx-ingress/nginx-config was updated

• check content of /etc/nginx/nginx.conf in the NIC pod

nginx@nginx-ingress-68449896cb-4jjpp:/etc/nginx$ head nginx.conf
worker_processes  auto;

daemon off;

error_log  stderr notice;
pid        /var/lib/nginx/nginx.pid;
load_module modules/ngx_fips_check_module.so;

load_module modules/ngx_http_js_module.so;

• apply custom main-template using ConfigMap
  beginning of the custom main-template

➜  common git:(fix/github-5906) ✗ head nginx-config-main-template-02.yaml
kind: ConfigMap
apiVersion: v1
metadata:
  name: nginx-config
  namespace: nginx-ingress
data:
  main-template: |
    # VERSION 2
    # main template from config map
    # this is a test

• verify the main template is applied

I20241015 12:15:56.435890   1 verify.go:90] success, version 4 ensured. took: 161.217208ms
I20241015 12:15:56.436318   1 controller.go:262] Event(v1.ObjectReference{Kind:"ConfigMap", Namespace:"nginx-ingress", Name:"nginx-config", UID:"ae356055-5493-47fc-b107-5d16e7a71c10", APIVersion:"v1", ResourceVersion:"185894", FieldPath:""}): type: 'Normal' reason: 'Updated' Configuration from nginx-ingress/nginx-config was updated
2024/10/15 12:15:56 [notice] 78#78: exit

nginx@nginx-ingress-68449896cb-4jjpp:/etc/nginx$ head nginx.conf
# VERSION 2
# main template from config map
# this is a test
#
worker_processes  auto;
daemon off;
error_log  stderr notice;
pid        /var/lib/nginx/nginx.pid;
load_module modules/ngx_fips_check_module.so;
load_module modules/ngx_http_js_module.so;

➜  common git:(fix/github-5906) ✗ k describe configmaps -n nginx-ingress nginx-config
Name:         nginx-config
Namespace:    nginx-ingress
Labels:       <none>
Annotations:  <none>

Data
====
main-template:
----
# VERSION 2
# main template from config map
# this is a test
#
worker_processes  auto;
daemon off;
error_log  stderr notice;
pid        /var/lib/nginx/nginx.pid;
load_module modules/ngx_fips_check_module.so;
load_module modules/ngx_http_js_module.so;

events {
    worker_connections  1024;
}
. . . 

• remove the custom main-template from the ConfigMap obj (apply an empty ConfigMap)

➜  common git:(fix/github-5906) ✗ kaf nginx-config.yaml
configmap/nginx-config configured

➜  common git:(fix/github-5906) ✗ k describe configmaps -n nginx-ingress nginx-config
Name:         nginx-config
Namespace:    nginx-ingress
Labels:       <none>
Annotations:  <none>

Data
====

BinaryData
====

Events:
  Type    Reason   Age                From                      Message
  ----    ------   ----               ----                      -------
  Normal  Updated  51m (x9 over 21h)  nginx-ingress-controller  Configuration from nginx-ingress/nginx-config was updated
  Normal  Updated  60s (x5 over 44m)  nginx-ingress-controller  Configuration from nginx-ingress/nginx-config was updated

• verify /etc/nginx/nginx.conf is reverted back to the original config file

nginx@nginx-ingress-68449896cb-4jjpp:/etc/nginx$ head nginx.conf
worker_processes  auto;

daemon off;

error_log  stderr notice;
pid        /var/lib/nginx/nginx.pid;
load_module modules/ngx_fips_check_module.so;

load_module modules/ngx_http_js_module.so;

[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 53.24%. Comparing base (5d85ad8) to head (2e94d36).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/configs/configmaps.go	50.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6661      +/-   ##
==========================================
+ Coverage   53.01%   53.24%   +0.22%     
==========================================
  Files          87       87              
  Lines       20053    20063      +10     
==========================================
+ Hits        10632    10683      +51     
+ Misses       9008     8950      -58     
- Partials      413      430      +17     

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